The subject matter herein relates generally to insert flow meters, and, more particularly, to an improved insert flow meter capable of measuring the physical characteristics of a flow comprising more than one phase of matter, for example liquid and gas, also known as a multiphase flow meter.
Flow meters provide critical measurements concerning the characteristics of a flow within a pipe, for example the rate and volume of material flowing through the pipe, as well as pressure, temperature and other measurements. This is especially true in industrial applications, such as those in which a flowmeter is used to measure material flow in a chemical processing or petroleum refining plant. The data produced is used to not only monitor and quantify the plant output, but to evaluate overall plant conditions and operational performance. Insert meters placed within these industrial systems must therefore be robust in nature in order to function in the severe environments experienced in various plant applications, for example within widely varying temperature extremes, high flow rates, and high pressure, while producing highly accurate measurements in order to properly quantify production levels and assess operational characteristics.
Several devices are currently used to perform flow measurements in industrial applications. For example, in one solution, pressure sensors are placed along one or more cone-shaped plugs positioned in the center of a pipe. The plug occupies a portion of the pipe diameter through which the flow travels, thereby causing a disturbance in the flow as the material moves past. By measuring the differential pressures around the plug, the flow rate can be determined. The shape of the plug is chosen to enhance selected flow characteristics that cause the pressure differentials as the material flows past the contours of the plug. One limitation of this approach is that manipulating the flow using the plug can require a substantial length of straight pipe. This can create difficulties and increase costs in industrial applications, such as in a refinery, in which complicated networks of pipes and other equipment can limit the available space. In instances where the insert meter is retrofitted within an existing pipe network, retrofitting the system to accommodate a new meter can be time consuming and costly, especially in high pressure systems where the pipe wall can be very thick and made with expensive materials.
Other solutions employ an orifice plate having pressure sensors that extend into the flow within the pipe to create a partial blockage of the flow and measure pressure. Because insert meters employing plugs or orifice plates are placed within a pipe and, by design, work to reduce the area of the pipe to restrict flow in order to generate pressure differentials from which the flow rate is determined, such meters diminish the efficiency of the piping network. In turn, additional energy is required to transport the same amount of material as an unobstructed system would require, thereby increasing operational costs.
Furthermore, measurement accuracy can be dependent on positioning the plug or orifice plate in the center of the pipe, which can be difficult to correctly establish and maintain over time in industrial environments. Additionally, use of a centralized plug that restricts flow can result in build up of material and eventual clogging of the pipe over time, or, in extreme cases, rupture of the pipe and fittings. In high flow or high pressure environments, the suspended plug or orifice plate, or the components attached thereto, might break free and be carried along in the flow, causing damage to downstream components within the system.
Lastly, the technique of determining the flow rate from pressure differentials cannot distinguish between different phases of matter, for example liquid and gas. Many industrial applications often transport materials that comprise more than one phase of matter. Accordingly, in situations in which such a multiphase flow is present, for example as in a petroleum refinery where both liquid crude oil and natural gas may be present, insert flow meters are unable to determine the content of the flow and the volume of each component being transported within the pipe. Inaccurately determining the content of the flow can lead to problems in downstream systems that are dependent on the upstream flow calculations, and can also result in inaccurate valuations of the flow content, for example, in a situation where the crude oil being measured contains high natural gas content.
It would be advantageous to provide an insert flow meter that is not only mechanically robust and capable of being retrofitted into and operating in the limited space and severe environments experienced in industrial applications, but which also provides highly accurate measurements of flow characteristics, and which is capable of differentiating between the different phases of matter present in the flow.